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Preparation of semi-solid AlSi7Mg alloy slurry with big capability

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Rare Metals 2010年第6期29卷 642-645页

作者： LI Sha and MAO Weimin school of materials science and engineering,university of science and technology Beijing,Beijing 100083,china school of materials science and engineering University of Science and Technology Beijing Beijing China

Semi-solid AlSi7Mg alloy slurry was prepared by low superheat pouring and weak traveling-wave electromagnetic *** effects of pouring temperature and stirring power on the microstructure of AlSi7Mg alloy slurry were *** results show that the semi-solid AlSi7Mg alloy slurry of 5 kg can be *** new technology can save energy and make the pouring process *** the pouring temperature is decreased at a stirring power of 0.41 kW,the shape of primary α-Al grains gradually changes from dendritic-like to *** the alloy melt is poured at the temperature（630°C） with a certain superheat,the pouring process becomes easier,and the spherical microstructure of AlSi7Mg alloy slurry can be prepared by the weak traveling-wave electromagnetic *** the pouring temperature is 630°C,increasing the stirring power appropriately can result in better spherical primary α-Al grains,but if the stirring power is increased to a certain value（1.72 kW）,the shape of primary α-Al grains does not obviously improve when the stirring power is continually increased.

关键词： aluminum alloys metal forming semisolid slurry electromagnetic stirring microstructure

Quantum properties of the binomial state field interacting with a two-level atom

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science china(Physics,Mechanics & Astronomy) 2010年第5期53卷 864-869页

作者： JIANG DaoLai,REN XueZao,CONG HongLu & LI Lei school of science,southwest university of science and technology,mianyang 621010,china 1. school of science Southwest University of Science and Technology Mianyang 621010 China

By the method of coherent-state orthogonalization expansion,the atomic inversion and the anti-bunching effect in a two-level atomic system interacting with binomial state field are studied under the Jaynes-Cummings model without rotating wave *** influence of the parameter and the detuning on the anti-bunching effect are discussed,and the anti-bunching effect is also discussed under the conditions of strong *** studies show that the second order coherence degrees are quite different between the situations of with and without-rotating wave *** the latter when the detuning increases,the duration of the bunching effect increases at the beginning and then decreases,and finally the light field displays anti-bunching effect completely.

关键词： coherent state orthogonalization expansion binomial state field Jaynes-Cummings model without-rotating wave approximation atomic inversion

Sol-gel Preparation and Infrared Radiation Property of Boron-substituted Cordierite Glass-ceramics

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Journal of materials science & technology 2010年第5期26卷 445-448页

作者： Shuming Wang and Fenghua Kuang school of materials science and engineering,university of science & technology Beijing,Beijing 100083,china [a] school of materials science and engineering university of science & technology Beijing Beijing 100083 china

Boron for aluminum substitution in the cordierite structure has been examined by sol-gel preparation of different samples along the compositional junction Mg2Al4-xBxSi5O18 with x=0,0.5,1,*** increasing the x value from 0 to 1.5 the crystallization behavior changed *** amount B2O3 doping can promote the sintering of amorphous cordierite gel,effectively restrain the precipitation of μ-cordierite and enhance the crystallization of α-*** substitution of B3＋ for Al3＋ in cordierite crystal structure can effectively improve the near-infrared spectral emissivity of this cordierite based glass-ceramics.

关键词： Sol-gel Glass-ceramics Infrared radiation B3+ substitution Solid solution

Dislocation Densites of Deformed Steel Sheets Based on Positron Annihilation

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International Journal of Minerals,Metallurgy and materials 1998年第1期12卷 47-50页

作者： Yonglin Kang Xianjin Wang (materials science and engineering school, university of science and technology Beijing, Beijing 100083, china) materials science and engineering school University of Science and Technology Beijing Beijing 100083 China

The variation regularity of dislocation densites of some deformed steel sheets under three kinds of strainpaths as uniaxial tension, plane strain and equal biaxial stretching was investigated by means of positron lifetimespectrum and Doppler-broadening techniques. The results show that the increasing rate of dislocation densites isrelated to the plastic strain path. A relationship between the increasing rate of micro-defects, macro-instability andforming limits during the process of steel sheet forming was got based on analyzing the mechanism of dislocationdensity increasing under different stress-strain condihons.

关键词： positron annihilation dislocation steel sheet strain path

Application of mesoscale modeling optimization to development of advanced materials

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Progress in Natural science:materials International 2004年第8期14卷 8-15页

作者： SONG Xiaoyan(school of materials science and engineering, Beijing university of technology, Beijing 100022, china) Beijing Univ Technol Sch Mat Sci & Engn Beijing 100022 Peoples R China

The rapid development of computer modeling in recent years offers opportunities for materials preparation in a more economic and efficient way. In the present paper, a practicable route for research and development of advanced materials by applying the visual and quantitative modeling technique on the mesoscale is introduced. A 3D simulation model is developed to describe the microstructure evolution during the whole process of deformation, recrystallization and grain growth in a material containing particles. In the light of simulation optimization, the long-term stabilized fine grain structures ideal for high-temperature applications are designed and produced. In addition, the feasibility, reliability and prospects of material development based on mesoscale modeling are discussed.

关键词： mesoscale computer simulation Monte Carlo technique deformation recrystallization grain growth.

Effects of silver powder particle size on the microstructure and properties of Ag-Yb_2O_3 electrical contact materials prepared by spark plasma sintering

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Rare Metals 2010年第4期29卷 366-370页

作者： CHEN Xiaohua,JIA Chengchang,and LIU Xiangbing school of materials science and engineering,university of science and technology Beijing,Beijing 100083,china school of materials science and engineering University of Science and Technology Beijing Beijing China

mg-Yb203 electrical contact materials were fabricated by spark plasma sintefing （SPS）. The effects of silver powder particle size on the microstructure and properties of the samples were investigated. The surface morphologies of the sintered samples were examined by optical microscope （OM）, and the fracture morphologies were observed by scanning electron microscopy （SEM）. The physical and mechanical properties such as density, electrical resistivity, microhardness, and tensile strength were also tested. The results show that the silver powder particle size has evident effects on the sintered materials. Comparing with coarse silver powder （5 ktm）, homogeneous and fme microstmcture was obtained by fine silver powder （_〈0.5-1am）. At the same time, the electrical conductivity, microhardness, and tensile strength of the sin- tered samples with fine silver powder were higher than those of the samples with coarse silver powder. However, silver powder particle size has little influence on the relative densities, which of all samples （both by free and coarse silver powders） is more than 95%. The fracture characteristics are ductile.

关键词： composites electrical contact materials spark plasma sintering particle size microstructure physical properties mechanical properties

Three-Dimensional and Cross-sectional Characteristics of Normal Grain Growth Based on Monte Carlo Simulation

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International Journal of Minerals,Metallurgy and materials 1998年第3期12卷 129-133,139页

作者： Xiaoyan Song Guoquan Liu(Material science and engineering school, university of science and technology Beijing, Beijing 100083, china)(Department of materials science and engineering, Hebei university of technology, Tianjin 300130, china) Material science and engineering school University of Science and Technology Beijing Beijing 100083 China Departments of materials science and engineering Hebei University of Technology Tianjin 300130 China

An appropriate Monte Carlo method was developed to simulate the three-dimensional normal grain growth more completely. Comparative investigation on the three-dimensional and the cross-sectional characteristics of normal grain growth was done. It was found that the time exponent of grain growth determined from cross-section exhibits the same rule of increasing slowly with time and approaching the theoretical value n = 0.5 of steadygrain growth as the three-dimensional (3-D) system. From change of the number of grains per unit area with timemeasured in cross-section, the state of 3-D normal grain growth may be predicted. The gtain size distribution incross-section is different from that in 3-D system and can not express the evolution characteristic of the 3-D distribution. Furthermore, there exists statistical connection between the topological parameters in cross-section and thosein three-dimensions.

关键词： Monte Carlo simulation normal grain growth three-dimension cross-section characteristics

Production and Characterization of Spherical Porous Lignin Pellets

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稀有金属材料与工程 2011年第S3期40卷 188-192页

作者： Li Xianfa, Luo Xuegang southwest university of science and technology, mianyang 621010, china SW Univ Sci & Technol Mianyang 621010 Peoples R China

With industrial kraft lignin as precursors, the transformer oil as dispersive phase, addin sodium dodecyl sulfate as dispersant and epichlorohydrin as crosslinking agent, the spheric porous lignin pellets were produced by two-phase solvent system. The suitable process conditions of producing the lignin pellets were determined by signal-factor and orthogonal experiments. The lignin pellets were characterized by scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), thermogravimetry and X-ray diffraction analysis. The results show that the ideal spherical lignin pellets with 87.75% of the yield could be obtained under the such conditions as 5 g lignin dissolved in 50 ml water by adjusting the solution pH value to 13, 0.6 g sodium dodecyl sulfate, 3 g epichlorohydrin and 150 ml transformer oil. Morphology studies show that lignin pellets have the full spheric shape and inner porous microstructure. Evidence for the reaction between lignin and epichlorohydrin has been observed using FT-IR and thermogravimetric analysis. The results of X-ray diffraction analysis demonstrate that crosslinked lignin pellets mainly are an amorphous polymer.

关键词： Kraft lignin two-phase solvent system spherical porous lignin pellets

Effect of powder mixing process on the microstructure and thermal conductivity of Al/diamond composites fabricated by spark plasma sintering

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Rare Metals 2010年第1期29卷 86-91页

作者： CHU Ke, JIA Chengchang, LIANG Xuebing, and CHEN Hui school of materials science and engineering, university of science and technology Beijing, Beijing 100083, china school of materials science and engineering University of Science and Technology Beijing

Two powder mixing processes, mechanical mixing （MM） and mechanical alloying （MA）, were used to prepare mixed Al/diamond powders, which were subsequently consolidated using spark plasma sintering （SPS） to produce bulk Al/diamond composites. The effects of the powder mixing process on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated. The results show that the powder mixing process can significantly affect the microstructure and the thermal conductivity of the composites. Agglomerations of the particles occurred in mixed powders using MM for 30 min, which led to high pore content and weak interfacial bonding in the composites and resulted in low relative density and low thermal conductivity for the composites. Mixed powders of homogeneous distribution of diamond particles could be obtained using MA for 10 min and MM for 2 h. The composite prepared through MA indicated a high relative density but low thermal conductivity due to its defects, such as damaged particles, Fe impurity, and local interfacial debonding, which were mainly introduced in the MA process. In contrast, the composite made by MM for 2 h demonstrated high relative density and an excellent thermal conductivity of 325 W.m^-1.K^-1, owing to its having few defects and strong inter-facial bonding.

关键词： metal matrix composites thermal properties sintering powder mixing